The invention relates to a method and apparatus for effecting error free transmission of digital data through a medium, such as air, between a transmitter and a receiver. The invention will be described herein with reference to its use in ultrasonic transmitter/receiver applications although those skilled in the art will recognize that its application is not so limited.
Ultrasonic signals transmitted between a transmitter and receiver travel many different paths. These different paths result from reflections of the signal from other sources in the medium. As a result the signal ultimately received by the receiver may be reinforced or canceled in certain portions depending on the phase relationship between the transmitted and reflected signal.
Ultrasonic transmitter/receiver systems have myriad applications. For example, systems are used as audiovisual remote controls, garage door openers, and security systems. Certain applications of such systems require data to be transmitted between the transmitter and receiver to accomplish programming tasks in apparatus connected to the receiver circuitry.
Many factors may contribute to such signal degradation. The main source of such degradation arises from reflection of the transmitted signal between the source and the receiver. Such reflections may result from any object in the transmission medium. Reflections of the signal result in the receipt of the same transmitted signal more than once sometimes referred to as echoes or path delays. The signal received is thus reinforced or canceled in certain areas and the integrity of the signal is, consequently, compromised.
Another source of signal degradation is the generation of spurious signals generated by other transmission apparatus such as those used in burglar alarms and automatic garage door openers, or merely from the jangling of a set of keys. These spurious signals result in the problems similar to those caused by reflections.
It is thus desirable to discriminate the data encoded in the transmitted signal from the degraded, received signal. The importance of such discrimination increases proportionately with the complexity of the data required in the particular application.
The preferred application of the method and apparatus of the invention is in a remote control hearing aid system. In such a system, the discrimination method makes it possible to program a hearing aid device, such as one used in-the-ear of the user, with a set of customized parameters particular to the user's own hearing problems to optimize the hearing enhancement characteristics of the device.
In the hearing aid art, systems are known in which the volume of the hearing device is adjustable in incremental steps from a remote control mechanism while the device is in the user's ear. The invention allows for a system wherein complex programming parameters may be transmitted to the receiver circuit to allow for the user to change the characteristics of the hearing aid between several different operational situations. For example, the aid itself can be programmed with a set of parameters to provide optimal performance for the user in situations where the user is in a noisy, crowded room. In addition, the aid can be programmed for situations where the user is in a quiet environment which requires discrimination of slight sounds. The invention allows such programming to occur from a remote control transmitter under the user's control within a wide range of distance and position from the hearing aid. The invention ensures that the data received by the device are only that data required to complete the programming.
The invention is useful in such a system in allowing programming codes to be transmitted between the remote control unit and the hearing device. It will be apparent to those skilled in the art that numerous possible applications for the system exist.
Thus, an object of the invention is to provide an improved method and apparatus for discriminating the data contained in a transmitted signal out of a corrupted received signal wherein the received signal may be corrupted by reflections and spurious signals.
A further object of the invention is to provide an improved method and apparatus to compensate for signal reflections and path length differences in the received signal.
A further object of the invention is to provide an improved method and apparatus to compensate for spurious signals which may be encountered and received by the receiver.
Other objects of the invention will become apparent to those skilled in the art from the following description and the accompanying drawings.